Since a semiconductor laser element generates heat during operation, the temperature of the element rises. Here, it is known that the lifetime of the semiconductor laser element decreases as the temperature rises. Accordingly, in order to achieve a long lifetime of the semiconductor laser element, it is required that the temperature of the element is not more than a fixed required temperature. From such a viewpoint, in general, a laser light source device including a semiconductor laser element is provided with a cooler for cooling the semiconductor laser element. In the following description, the “temperature of the semiconductor laser element” refers to the temperature during operation of the semiconductor laser element.
Patent Document 1 discloses a laser light source device including a Peltier element as an example of the above-described cooler. The laser light source device includes a measurer for measuring the temperature of the semiconductor laser element. A current value to be supplied to the Peltier element is controlled so that the temperature of the semiconductor laser element measured by the measurer is stabilized within not more than a fixed required temperature range. Specifically, in the laser light source device of Patent Document 1, control is performed to increase the current value to be supplied to the Peltier element as the measured temperature of the semiconductor laser element is higher.